Propagation of discontinuouswaves along a dry bed

The possibility of simulating the process of propagation of discontinuous waves along a dry bed on the basis of the equations of the first approximation of shallow water theory is studied. It is shown that the consistent losses of the free-stream total momentum and energy can be found from the mass conservation law within the framework of the shallow water equations. As an example, solutions of the problem of dam break with a dry bed in the lower pool and the problem of impingement of a discontinuous wave on a coastal shelf are constructed. These exact solutions are compared with the results of laboratory experiments.     

Propagation of nonlinear waves along a viscoelastic bar

Various types of nonlinear waves propagating along a viscoelastic bar are considered. The rheological equation of state has strong physical and geometric nonlinearities, and nonisothermal effects are included. Both weak (isentropic) and shock waves of loading and unloading are investigated. It is shown that, for certain rubber-like materials, stable shock waves of extension can exist along with the shock waves of compression at very large strains. We then consider the strike of a viscoelastic bar of finite length against a rigid obstacle. Numerical solutions to this problem illustrate the influence of stress relaxation on nonlinear wave processes. A model for sticking and bouncing off is formulated and the mass-averaged velocity of the bar at the moment when it bounces off the obstacle is calculated.     

Propagation properties of optical soliton in an erbium-doped tapered parabolic index nonlinear fiber: soliton control

In this paper, with the aid of symbolic computation, we investigate the generalized nonlinear Schrödinger Maxwell–Bloch equation, which describes the propagation of the optical soliton through an inhomogeneous two-level dielectric tapered fiber medium. By virtue of the Darboux transformation method, two-soliton solutions are generated based on the constructed Lax pair and figures are plotted to illustrate the properties of the obtained solutions. Moreover, through manipulating the dispersion and nonlinearity profiles, various soliton control systems are investigated which is promising for potential applications in the design of soliton compressor, soliton amplification and high-speed optical devices in ultralarge capacity transmission systems. This means that we are able to control the soliton types with suitably selected values of the parameters. Additionally more soliton control techniques are proposed and investigated. We expect that the above analysis could be observed in future experiments.     

充液弯管连续/离散模型振动的动刚度解法

由充液弯管三维振动模型切入,应用动刚度法构建了弯管及直管单元的振动求解方法,进而用于组装求解充液管系的振动,可同时适用于含弯管单元的连续模型或只含直管单元的离散模型;通过算例对比,证明动刚度法比传递矩阵法和有限元法在计算效率和精度上有所提升;与充液L型管道振动实验测得的加速度频响曲线对比,验证了本文对于管道组装的计算方法的有效性,此外还分析了连续模型和离散模型的区别及适用范围。     

Dynamics of a fluid-filled curvilinear pipeline

A mathematical model is presented, and numerical experiments are performed to describe the mechanics of the slow movement of a pipeline. The problem reduction algorithm to one-dimensional formulation is offered. Results of numerical experiment for the model problem are adduced. The proposed mathematical model is found to adequately describe the dynamics of known phenomena of pipes. The cross-sections of the extended curvilinear thin-walled pipeline are numerically demonstrated to experience warping, which has experimental confirmation in the literature.     

Propagation of longitudinal deformation wave along a lifting rope of variable length

The problem of motion of the rope of variable length consists of solving the boundary value problem with a variable boundary for the one-dimensional wave equation. A change of the rope length is caused by the force acting at the upper cross section of the rope. Studying the wave propagation process along the rope is based on the known integro-differential relation. The problem is reduced to solving two ordinary differential equations with a retarded argument that describe the variable length of the rope and the position of its lower end. The value of argument for functions involved in the right-hand side of the equations lag behind the argument value in the left-hand side of the equations by a time interval it takes for a propagation of the deformation wave throughout the current rope length. The problem is solved by using a technique of the sequential continuation of solution in the cyclic mode for each of the equation alternately. A computer realization of this technique presents no problem. A pilot computer program has been developed for solving the problem. Results of the numerical solution are presented in the case that the active force varies with time according to a piecewise linear relation.     

多层电磁弹性圆柱壳内波的轴向传播

对多层电磁弹性圆柱壳内波的轴向传播进行了分析。根据柱坐标系下电磁弹性多层结构的几何方程、平衡方程和本构方程,推导出了两个层间变量所满足的状态方程。通过状态方程的解和层间变量连续性条件,得到了多层圆柱体内外表面层间变量的传递关系。最后利用边界条件,导出了波在传播时所满足的频散方程,并求得该结构的模态参数。以一个三层的压电/压磁材料组成的柱壳结构作为数值算例,计算出波在其中轴向传播时的频散关系和模态参数,并对计算结果进行了分析。     

Propagation of acoustic perturbations along a supersonic jet flowing out into the atmosphere

The propagation of acoustic perturbations (specified in the outlet cross section of a particular channel) along a supersonic jet flowing out of the channel is considered; also considered is acoustic emission from the surface of the jet into the atmosphere. The solution of these problems is obtained by a numerical method on the linear approximation. The laws governing the propagation of the perturbations as a function of the perturbation frequency and other determining parameters are investigated; these parameters include the velocity and temperature of the jet, the velocity of the subsonic accompanying flow in the external medium, and the character of the perturbation in the initial cross section of the jet.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 92–99, March–April, 1977.     

Localization of wave motions in a fluid-filled cylinder

The properties of harmonic surface waves in a fluid-filled cylinder made of a compliant material are studied. The wave motions are described by a complete system of dynamic equations of elasticity and the equation of motion of a perfect compressible fluid. An asymptotic analysis of the dispersion equation for large wave numbers and a qualitative analysis of the dispersion spectrum show that there are two surface waves in this waveguide system. The first normal wave forms a Stoneley wave on the inside surface with increase in the wave number. The second normal wave forms a Rayleigh wave on the outside surface. The phase velocities of all the other waves tend to the velocity of the shear wave in the cylinder material. The dispersion, kinematic, and energy characteristics of surface waves are analyzed. It is established how the wave localization processes differ in hard and compliant materials of the cylinder __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 4, pp. 72–86, April 2008.     

Propagation of harmonic waves along a cylindrical cavity in a compressible medium with initial stresses

Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Prikladnaya Mekhanika, Vol. 26, No. 2, pp. 31–36, February, 1990.     

Settling of discs inside a vertical fluid-filled tube

The broadside settling of discs along the centerline of a fluid-filled tube is studied. The Stokes equation is solved by a method of eigenfunction expansions and collocation. Depending on the geometry, the flow field shows different arrangements of recirculating eddies. Due to mutual shielding, the discs settle faster when they are closer together.     

Propagation of surface acoustic waves along the free boundary of a saturated porous medium

Frequency dependences of the velocity and attenuation coefficients of the waves propagating along a flat interface between a saturated porous medium and gas (vacuum) are studied. It is shown that the propagation of one or two surface modes is possible, depending on the parameters of the saturated porous medium and the conditions on the interface.     

Deformation of a fluid-filled compliant cylinder in a uniform flow

We investigated surface compliance effects of a fluid-filled object in flow on its shape and internal flow through numerical simulation. A two-dimensional compliant cylinder containing fluid in a flow is a simple model of a cell, e.g. an erythrocyte, leukocyte or platelet. The thin membrane of the cylinder consisted of a network of mass-spring-damper (MSD) systems, representing its mechanical characteristics. We assumed that the stiffness and damping coefficients were those of latex gum. The two-dimensional flow inside and outside the membrane was obtained by solving the two-dimensional Navier–Stokes equations by using the finite element scheme at Re=400, based on the external flow velocity and diameter of an initial circular cylinder. The deformation of the membrane was calculated by solving the equation of motion for an MSD system by using the fourth-order Runge-Kutta method. The compliant cylinder deformed more if its stiffness was smaller than that of latex gum. The initial circular section of the cylinder became oval, with a flat front and a convex rear. The aspect ratio of the lateral to streamwise axis length of the oval became larger than unity, and increased with decreasing stiffness. The drag coefficient of the oval cylinder became larger than that of the circular cylinder, and increased with decreasing stiffness. The partial vibration at the rear, caused by shedding vortices, induced oscillating internal flows between two antinodes of the vibrating membrane. Since the object with smaller stiffness had higher ductility, velocity fluctuations of the external flow influenced the internal flow of the compliant object through deformation of the membrane.     

The motion of a closely-fitting sphere in a fluid-filled tube

Singular perturbation techniques are used to investigate the slow, asymmetric flow around a sphere positioned eccentrically within a long, circular, cylindrical tube filled with viscous fluid. The results apply to situations in which the sphere occupies virtually the entire cross section of the cylinder, so that the clearance between the particle and tube wall is everywhere small compared with both the sphere and tube radii. The technique is an improvement over conventional “lubrication-theory” analyses.Asymptotic expansions, valid for small dimensionless clearances, are obtained for the hydrodynamic force, torque and pressure drop for flow past a stationary sphere, as well as for the case of a sphere translating or rotating in an otherwise quiescent fluid. These expansions are employed to predict the macroscopic behavior of both a neutrally-buoyant sphere suspended in a Poiseuille flow, and a sedimenting sphere in a vertical tube.The results find application in capillary blood flow, pipeline transport of encapsulated materials, and falling-ball viscometers.     

Transient radiation by a submerged fluid-filled cylindrical shell

The radiation by a submerged fluid-filled cylindrical shell in response to a transient external pressure pulse is considered, and a semi-analytical model based on the Reissner–Mindlin shell theory is employed to simulate the interaction numerically. Two types of radiated waves that have been previously seen in experimental images for a submerged evacuated cylindrical shell are observed in both the external and internal fluids, the symmetric Lamb waves S₀ and the antisymmetric Lamb (or pseudo-Rayleigh) waves A₀. The third type of radiated waves is also observed that has not been explicitly imaged either experimentally or numerically for a submerged evacuated cylindrical shell, and it is demonstrated that these waves are the Scholte–Stoneley waves A. The effect that the complex structure of the radiated field has on the wave phenomena in the internal fluid is analyzed for shells of several different thicknesses, and the results of this analysis are summarized in the form of diagrams suitable for the use at the pre-design stage.     

Smooth soliton and kink solutions for a new integrable soliton equation

Nonlinear Dynamics - We establish a relationship between a new integrable soliton equation and Gardner’s equation by a transformation. Then, we use this transformation and solutions of...     

The stability of a fluid-filled top rotating on a horizontal plane

Summary The stability of a fluid-filled top rotating on a rough horizontal plane about the erect axis is discussed and a stability criterion in analytical form is obtained. A sufficient condition of stability for a fluid-filled Chaplygin sphere is proved by using Lyapunov's direct method, and a more satisfactory explanation to Kelvin's question considering the influence of gravity and sliding friction is given. The fluid-filled Lagrange gyro is discussed as a special case when the plane is absolutely smooth.

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Stabilität eines flüssigkeitsgefüllten Kreisels auf horizontaler Unterlage

Übersich Für einen flüssigkeitsgefüllten Kreisel auf einer rauhen, horizontalen Unterlage wird die Stabilität um die Hochachse erörtert und ein Stabilitätskriterium in analytischer Form gewonnen. Mit Hilfe von Ljapunovs direkter Methode wird eine hinreichende Stabilitätsbedingung für eine flüssigkeitsgefüllte Chaplyginsche Kugel bewiesen und eine befriedigende Erklärung zu Kelvins Frage über den Einfluß von Schwerkraft und Gleitreibung gegeben. Der Lagrangesche Kreisel wird als Sonderfall mit glatter Unterlage behandelt.

     

Nonaxisymmetric interaction of a spherical radiator in a fluid-filled permeable borehole

The Biot theory of poroelasticity along with the proper cylindrical/spherical wave-field transformations are used to investigate general (nonaxisymmetric) harmonic radiation from a spherical surface vibrating at the center of a fluid-filled circular cylindrical cavity embedded within a fluid-saturated porous elastic formation. This configuration, which is a realistic idealization of an acoustic logging tool suspended in a fluid-filled borehole, is of practical importance with a multitude of possible applications in seismic engineering and geophysics. The analytical results are illustrated with numerical examples in which the spherical source suspended at the center of a water-filled borehole embedded within water-saturated soils of distinct frame properties (i.e., soft or stiff soils), is excited in vibrational modes of various orders. The basic acoustic and elastic field quantities such as the resistive/reactive components of the modal acoustic radiation impedance load as well as the radial displacement and stress components induced within the surrounding formation for a pulsating (n = 0), an oscillating (n = 1), and a quadrupole-like (n = 2) spherical source are evaluated and discussed for representative values of the parameters characterizing the system. Special attention is paid to the effects of source excitation frequency, size, surface velocity profile, and internal impedance as well as soil type on the modal impedance values and the displacement/stress amplitudes. Limiting cases are considered and fair agreements with well-known solutions are obtained.